Stent mandrel fixture and method for reducing coating defects

ABSTRACT

A stent mandrel fixture for supporting a stent during the application of a coating substance is provided.

This application is a divisional application of U.S. application Ser. No. 10/255,913, filed Sep. 26, 2002, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates generally to stent mandrel fixtures, and more particularly, but not exclusively, provides a stent mandrel fixture and method for reducing coating defects on stents.

BACKGROUND

Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of affected vessels. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.

FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. Struts 12 and connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.

Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.

One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent strut surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.

A shortcoming of the above-described method of medicating a stent is the potential for coating defects. While some coating defects can be minimized by adjusting the coating parameters, other defects occur due to the nature of the interface between the stent and the apparatus on which the stent is supported during the coating process. A high degree of surface contact between the stent and the supporting apparatus can provide regions in which the liquid composition can flow, wick, and collect as the composition is applied. As the solvent evaporates, the excess composition hardens to form excess coating at and around the contact points between the stent and the supporting apparatus. Upon the removal of the coated stent from the supporting apparatus, the excess coating may stick to the apparatus, thereby removing some of the coating from the stent and leaving bare areas. Alternatively, the excess coating may stick to the stent, thereby leaving excess coating as clumps or pools on the struts or webbing between the struts.

Accordingly, a new stent mandrel fixture is needed to minimize coating defects.

SUMMARY

In accordance with one embodiment, a stent mandrel fixture for supporting a stent during application of a coating substance to the stent is provided, comprising: a first member for supporting a first end of the stent, at least a portion of the first member being made from or being coated with a non-stick material for preventing the coating substance from adhering to the first member; a second member for supporting a second end of the stent, at least a portion of the second member being made from or being coated with the non-stick material; and a third member connecting the first member to the second member and extending through a longitudinal bore of the stent. The first or second member can have a domed shaped end, a flat end or can have grooves for receiving the coating substance. Examples of the non-stick material include poly (tetrafluor ethylene), fluorinated ethylene propylene, poly (vinylidene fluoride), poly (para-xylyene), and polyolefin.

In accordance with another embodiment of the invention, a stent mandrel fixture for supporting a stent during application of a coating substance to the stent is provided, comprising: a first member for contacting a first end of the stent, the first member having a domed shaped end; a second member for contacting a second end of the stent, the second member having a domed shaped end; and a third member connecting the first member to the second member and extending through a longitudinal bore of the stent, wherein the stent can be securely pinched between the domed shaped ends of the first and second members.

In accordance with yet another embodiment of the invention, a stent mandrel fixture for supporting a stent during application of a coating substance to the stent is provided, comprising: a first member for contacting a first end of the stent, the first member having a flat end; a second member for contacting a second end of the stent, the second member having a flat end; and a third member connecting the first member to the second member and extending through a longitudinal bore of the stent, wherein the stent can be securely pinched between the flat ends of the first and second members.

In accordance with another embodiment of the invention, a stent mandrel fixture for supporting a stent during application of a coating substance to the stent is provided, comprising: a first member for contacting a first end of the stent, the first member having grooves for receiving the coating substance; a second member for contacting a second end of the stent, the second member having grooves for receiving the coating substance; and a third member connecting the first member to the second member and extending through a longitudinal bore of the stent, wherein the stent can be securely pinched between the ends of the first and second members. In one embodiment, the first or second member is coned shape and the grooves extend longitudinally across the cone. In another embodiment, the grooves extend around the perimeter of the cone.

In accordance with another aspect of the invention, methods of coating a stent using the above-described fixtures are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

FIG. 1 illustrates a conventional stent;

FIG. 2 illustrates a stent mandrel fixture in accordance with an embodiment of the invention;

FIG. 3 illustrates an expanded view of stent mandrel fixture of FIG. 2;

FIG. 4 illustrates a cross section of a second embodiment of a stent mandrel fixture;

FIG. 5 illustrates a cross section of a third embodiment of a stent mandrel fixture;

FIG. 6 illustrates a cross section of a fourth embodiment of a stent mandrel fixture; and

FIG. 7A illustrates a cross section of a fifth embodiment of a stent mandrel fixture;

FIG. 7B illustrates a perspective view of the fifth embodiment of the stent mandrel fixture; and

FIG. 8 illustrates a perspective view of a sixth embodiment of a stent mandrel fixture.

DETAILED DESCRIPTION

The following description is provided to enable any person having ordinary skill in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles, features and teachings disclosed herein.

FIG. 2 illustrates a stent mandrel fixture 20 in accordance with an embodiment of the invention. Fixture 20 for supporting stent 10 is illustrated to include a support member 22, a mandrel 24, and a lock member 26. Support member 22 can connect to a motor 30A so as to provide rotational motion about the longitudinal axis of stent 10, as depicted by arrow 32, during a coating process. Another motor 30B can also be provided for moving support member 22 in a linear direction, back and forth, along a rail 34.

FIG. 3 illustrates an expanded view of stent mandrel fixture 20. Support member 22 includes a coning end portion 36, tapering inwardly at an angle φ₁ of about 15° to about 75°, more narrowly from about 30° to about 60°. By way of example, angle φ₁ can be about 45°. In accordance with one embodiment of the invention, mandrel 24 can be permanently affixed to coning end portion 36. Alternatively, support member 22 can include a bore 38 for receiving a first end 40 of mandrel 24. First end 40 of mandrel 24 can be threaded to screw into bore 38 or, alternatively, can be retained within bore 38 by a friction fit. Bore 38 should be deep enough so as to allow mandrel 24 to securely mate with support member 22. The depth of bore 38 can also be over-extended so as to allow a significant length of mandrel 24 to penetrate or screw into bore 38. Bore 38 can also extend completely through support member 22. This would allow the length of mandrel 24 to be adjusted to accommodate stents of various sizes.

The outer diameter of mandrel 24 can be smaller than the inner diameter of stent 10 so as to prevent the outer surface of mandrel 24 from making contact with the inner surface of stent 10. A sufficient clearance between the outer surface of mandrel 24 and the inner surface of stent 10 should be provided to prevent mandrel 24 from obstructing the pattern of the stent body during the coating process. By way of example, the outer diameter of mandrel 24 can be from about 0.010 inches (0.254 mm) to about 0.017 inches (0.432 mm) when stent 10 has an inner diameter of between about 0.025 inches (0.635 mm) and about 0.035 inches (0.889 mm).

Lock member 26 includes a coning end portion 42 having an inwardly tapered angle φ₂. Angle φ₂ can be the same as or different than the above-described angle φ₁. A second end 44 of mandrel 24 can be permanently affixed to lock member 26 if end 40 is disengagable from support member 22. Alternatively, in accordance with another embodiment, mandrel 24 can have a threaded second end 44 for screwing into a bore 46 of lock member 26. Bore 46 can be of any suitable depth that would allow lock member 26 to be incrementally moved closer to support member 22. Bore 46 can also extend completely through lock member 26. Accordingly, stents 10 of any length can be securely pinched between support and lock members 22 and 26. In accordance with yet another embodiment, a non-threaded second end 44 and bore 46 combination is employed such that second end 44 can be press-fitted or friction-fitted within bore 46 to prevent movement of stent 10 on stent mandrel fixture 20.

In order to reduce coating defects, ends 36 and 42 may be coated with one or more polymeric materials having less adhesive force with the coating substance than with members 22 and 26. Examples of a suitable polymeric materials include poly (tetrafluor ethylene) (e.g., Teflon®), fluorinated ethylene propylene (“FEP”), poly (vinylidene fluoride) (“PVDF”), poly (para-xylyene), polyamide (Nylon), polyolefins (e.g., high density poly (ethylene) and poly (propylene)), and polyacetal (Delrin®). In an alternative embodiment of the invention, members 22 and 26 may be made of one or more of the non-stick polymeric materials.

FIG. 4 illustrates a cross section of a second embodiment of a stent mandrel fixture 400. Fixture 400 includes a support member 410, a mandrel 420, and a lock member 430. Support member 410 and lock member 430 each have symmetrical ends 440 having surfaces 450 a and 450 b having a radius of curvature to minimize coating defects by minimizing contact between fixture 400 and stent 10. Curved surfaces 450 a and 450 b are in essence domed cylindrical protrusions instead of the conical shaped configuration of FIG. 2 and FIG. 3. Curved surface 450 a engages one end of stent 10 and curved surface 450 b engages the other end of stent 10 so that stent 10 is securely pinched there between. The diameter of curved surfaces 450 a and 450 b is greater than the outer diameter of stent 10 as positioned between support member 410 and lock member 430.

FIG. 5 illustrates a cross section of a third embodiment of a stent mandrel fixture 500. Fixture 500 includes a support member 510, a mandrel 520, and a lock member 530. Support member 510 and lock member 530 each have symmetrical ends 540 having surfaces 550 a and 550 b that have small surface changes. While surfaces 550 a and 550 b only show a single step, other embodiments of the invention may include surfaces each having a plurality of steps. The unevenness of surfaces 550 a and 550 b help minimize the formation of coating defects. Surface 550 a engages one end of stent 10 and surface 550 b engages the other end of stent 10 so that stent 10 is securely pinched there between. The area of surfaces 550 a and 550 b is greater than the outer diameter of stent 10 positioned between support member 510 and lock member 530.

FIG. 6 illustrates a cross section of a fourth embodiment of a stent mandrel fixture 600. Fixture 600 includes a support member 610, a mandrel 620, and a lock member 630. Support member 610 and lock member 630 each have symmetrical ends 640 having substantially flat surfaces 650 a and 650 b to minimize coating defects. Surface 650 a engages one end of stent 10 and surface 650 b engages the other end of stent 10 so that stent 10 is securely pinched there between. The area of surfaces 650 a and 650 b can be greater than the outer diameter of stent 10 positioned between support member 610 and lock member 630.

FIG. 7A illustrates a cross section of a fifth embodiment of a stent mandrel fixture 700. Fixture 700 includes a support member 710, a mandrel 720, and a lock member 730. Support member 710 and lock member 730 each have symmetrical coned ends 740 having groove designs or channels 750 to minimize coating defects. FIG. 7B illustrates a perspective of a portion of stent mandrel fixture 700. Coned end 740 has grooves or channels 750 circumscribing coned end 740. These grooves or channels 750 enable the flow of composition off coned ends 740 and are deep enough to receive excess composition applied during the coating process.

FIG. 8 illustrates a perspective view of a sixth embodiment of a stent mandrel fixture. Each end 840 has a grooved design to prevent coating defects from forming at the interface between stent 10 and end 840. Coned ends 840 have grooves or channels extending longitudinally from a distal end of coned end 840 to the proximal end of coned end 840. Any suitable number of channels 850 can be provided around the circumference of coned end 840. Grooves or channels 850 enable the composition to be collected in channels 850. Composition can flow off of coned ends 840, thereby minimizing coating defects.

The foregoing description of the preferred embodiments of the present invention is by way of example only, and other variations and modifications of the above-described embodiments and methods are possible in light of the foregoing teaching. For example, stent mandrel fixtures 400, 500, 600 and 700 may also be coated with a non-stick polymeric material having less adhesive force with the coating substance than with the members. 

1. A method of coating a stent with a substance, comprising: mounting a stent on a stent mandrel fixture, the stent including a first and second end, and a bore extending between the first and second ends, and the mandrel including a first member, second member and third member, the mounting step including the steps of placing the first end on the first member including placing the first end on a domed-shaped surface of the first member, disposing the third member within the bore of the stent, and placing the second end on the second member, wherein the disposing the third member step occurs before the placing the second end step; and applying the substance to the stent.
 2. The method of claim 1, the mounting step further including the step of connecting the second member to the third member after the placing the first end on the first member step.
 3. The method of claim 2, the mounting step further including the step of displacing the second member relative to the first member after connecting the second member to the third member.
 4. The method of claim 2, the mounting step further including the step of pinching the stent between the first member and the second member including the step of displacing one of the first and second members relative to the other.
 5. The method of claim 4, wherein the pinching step further includes the step of displacing the second member over a threading formed on the third member.
 6. The method of claim 4, wherein the pinching step further includes the step of pinching the stent between opposed surfaces, each of the surfaces forming a dome such that the stent is pinched between opposed domed shaped surfaces.
 7. The method of claim 1, wherein the contact area between the domed shaped surface and the stent traces a circle.
 8. The method of claim 1, wherein the first end is placed on a domed cylindrical protrusion of the first member.
 9. The method of claim 1 wherein a first portion of the domed shaped surface is within the stent bore and a second portion of the domed shaped surface is outside of the stent bore.
 10. A method of coating a stent with a substance, comprising: mounting a stent on a stent mandrel fixture, the stent including a first and second end, and a bore extending between the first and second ends, and the mandrel including a first member, second member and third member, the mounting step including the steps of placing the first end on the first member including placing the first end on a domed-shaped surface of the first member, disposing the third member within the bore of the stent, and placing the second end on the second member; and applying the substance to the stent, wherein the mounting step includes placing the first and second ends of the stent on a non-stick coating disposed on at least one of the respective first and second members. 